I don't think the girl's families would be sending posters out around the United States, handing out flyers at public events and going on tv shows like Dr. Phil and Megyn Kelly begging for tips if this was the case. Why would they waste their energy and resources appealing for information and tips if law enforcement told them we know who BG is and they were planning to arrest him soon? It doesn't make any sense to me.
One other possibility is, that LE is still issuing subpoenas based on tips they have received from the general public.
Pending on the information they are trying to acquire, it may take a search warrant rather than a subpoena, which would require to have probable cause. That may be a challenge in itself. So, they may have some good leads, but may not actually know, who they are dealing with.
: X is posting a youtube video wandering around the high bridge area prior to the murder. He is wearing some particular shoes in this video. After the murder, he goes ahead and edits his video by cutting out the part(s) showing his shoes, as they look just like the shoes BG was wearing. This has been noticed by Y, an online user. That person Y sends in a tip. Now LE has to figure out X's identity, if they decide it is worth following up on it. But can they get the Youtube poster's ID with a subpoena (no probable cause needed) or do they have to have a search warrant ( probable cause needed)? This would be an example of having a possible lead, but not necessarily being able to obtain the info - yet.